In Mortal Shell 2, Resin is a very useful special equipment item. The Breach Stone is one of the more unique types, increasing ranged toughness damage. Upgrading it provides a stable boost to toughness damage. To obtain this Resin, head to the Seeping Marsh, enter the Mushroom Village, and open a chest found within the village.
How to Obtain the Breach Stone Resin in Mortal Shell 2